Nanoengineered materials utilize diminutive features to enhance interface/surface properties and overcome limitation of conventional materials. In recent years, progress in this field has been directed towards the fabrication of complex layered nanostructures such as core/shell configurations and advanced assembly techniques for functional arrangements of nanoparticles. Both of these routes, while promising, are in the nascent stages of development largely due to the high level of accuracy and localization required when modulating composition or aligning nanomaterials. One unique structure that has recently emerged with demonstrated enhancement of optoelectronic properties and promise as precisely fabricated linear assemblages of nanoparticles for plasmon waveguides are nanoparticle embedded nanotubes or nanopeapods.
To date, nanopeapods have been fabricated by a limited number of techniques typically requiring either a microwave reactor or a nanoporous template. The former is a specific, complex method with stringent conditions and a solid husk with little evidence for dimensional control over the sheathing material or material variation. Of the template techniques there are three different approaches that have demonstrated feasibility in terms of material selection and dimensional control. The first method utilizes a template to fabricate multisegmented nanowires, which are subsequently coated by a nanometer thin porous silica shell using sol gel chemistry. The nanowire consists of alternating layers of noble/base metals (i.e. Au/Ni, Ag/Ni) allowing the more base metal to be chemically etched after the silica coating. The nanoparticle chain materials and dimensions for this process can be finely tuned since they are determined by electrodeposition of the metal segments and template pore size. The second approach employs a nanoporous alumina template or a nanowire as a template for atomic layer deposition (ALD). This process requires ALD of two metal oxide (or polymer) materials, an outer shell and inner sacrificial layer. In the case of the metal oxide template, metal nanowires are then electrodeposited into the double coated nanopores. After etching the template and sacrificial layer the intermediate structure, composed of a metal oxide nanotube partially filled with a metal nanowire, emerges. To delineate the metal nanowire into particles or rods, one can take advantage of the Rayleigh instabilities during the annealing process. The procedure is more general with greater material variety of the shell (metal oxides or polymer). The last technique also relies on electrodeposition to generate base/noble metal multilayered nanowires within an alumina template, but solid state reaction differentiates their approach from others. The solid state reaction creates a new tube material by diffusion of the base metal into the alumina template, where Kirkendall effects create the void spaces between the noble nanoparticles.
However, all of the previously described methodologies suffer from one common limitation; the inability to fabricate nanoparticle and shell structures from materials such as metal/semiconductor, p-type/n-type semiconductor, metal/metal, metal oxide/metal oxide, or ferromagnetic/nonmagnetic. Accordingly, it would be desirable to fabricate nanoparticle and shell structures from materials such as metal/semiconductor, p-type/n-type semiconductor, metal/metal, metal oxide/metal oxide, or ferromagnetic/nonmagnetic and introduce these fabricated nanoparticles and shell structures into a host of fundamentally important studies with applicability to thermoelectric materials, spintronics, nanosensors, and plasmonics. Additionally, it would be desirable to modulate nanowire/nanotube structures of the same composition offer an efficient route to study confinement effects within nanotubes.